This invention relates to a rotary valve assembly for a boosting type unit injector.
In a prior art assembly, with the rotation of a spool of a rotary valve, a fuel supply port open at the outer periphery of the spool is successively communicated with ports of the rotary valve each connected to the boosting type unit injector for each cylinder, whereby fuel is supplied from a fuel passage in the spool to each injector.
The outer periphery of the spool is formed with a drain groove communicating with a drain passage. The drain groove communicates with fuel supply ports each communicating with a boosting piston chamber of each boosting type unit injector, so that fuel after the operation of each unit injector is drained through the drain groove.
In the prior art, however, the drain groove of the rotary valve also serves as a metering groove. Therefore, when a boosting piston chamber is suddenly opened, high pressure fuel therein forms an impulsive wave to adversely affect other injectors during a metering stroke, thus resulting in instable metering.